If a test were to be carried out, it could be timed to coincide with US President Barack Obama's visit to South Korea, which begins on Friday, April 25. That date also marks the 82nd anniversary of the founding of the North Korean People's Army (KPA). Pyongyang has a habit of carrying out grand gestures such as long-range missile and nuclear tests on or close to key anniversaries relating to the ruling Kim family, the Korean Workers' Party, the military, and the state.

A new nuclear test would serve three purposes. Firstly, it would allow North Korea to fine tune its atomic warheads and gain more scientific information about its devices. Secondly, it would demonstrate Pyongyang's military power at a time of relative US geopolitical weakness. Thirdly, North Korean leader Kim Jong Un could once again demonstrate his hardline credentials at a time when the regime appears to be recovering from a power struggle following the execution of former Number 2 man Jang Song Thaek last December.

There is little the outside world can do to punish North Korea. However, there is also little that Pyongyang would gain from a new nuclear test. Each time it tests a new atomic device, the psychological shock impact is typically less than the previous one, and its provocations have almost become routine. This could change if the next bomb is a new or more powerful type of detonation, but even so, the world has largely learned to live with the North Korean nuclear threat. The bigger question is whether Pyongyang will initiate another war scare of the kind seen in March-April 2013, or a naval confrontation in the disputed West Sea area. The latter could trigger a bigger clash by miscalculation, if the South responds forcefully.